1. Field of the Invention
This invention relates to seals and, more particularly, to electrical conduit sealing fittings.
2. Description of Related Art
Seals are provided in conduit and cable systems to minimize the passage of gases and vapors and prevent the passage of flames therethrough.
Various requirements concerning seals are set forth in Article 501, Section 501-5, of the National Electric Code. One such requirement is that all fittings in Class 1, Division 1 (hazardous) applications must have threaded engagement with its mating conduit. Another requirement is that the seal be filled with a sealing compound. The compounds used in explosion-proof sealing fittings must resist the force of an explosion in the conduit system that could reach several thousand psi. The compounds must also be dense enough to minimize the passage of gases from one part of the conduit system to another. Still further, they must be highly resistant to a great variety of solvents and chemicals. Typically, sealing compound is poured into place, whereupon it solidifies and becomes very hard.
The various requirements discussed above for sealing fittings in Class 1, Division 1 (hazardous) applications make them very difficult to remove. When an occasion arises which requires such a seal to be removed (such as adding or replacing the wires in the conduit) it is common to break or cut open the sealing fitting, crumple the hard compound, pull all the wires out of the conduit, install a new fitting, repull the wires and pour new compound. Often more than one seal is involved in a single run of conduit. This type of work is very time consuming and expensive in direct labor and materials, as well as being costly in terms of system down time. Based on the foregoing, it should be clear that a need has developed for a sealing fitting that would allow a seal to be replaced in location such as hazardous Class 1, Division 1, locations without removing all the electrical conductors or deenergizing the electrical system.